Preparation of cyclic ethers



1968 P. N. RYLANDER ETAL 3,408,364

PREPARATION OF CYCLIC ETHERS Filed May 26, 1965 Minutes from StanINVENTORS Paul A4 Hylander I Duane 2. Steele 7/ M ATTORNEY Uni d S ksPam 1 PREPARATION oF CYCLIC ETH s I Paul N. Rylander and Duane R.Steele, Newark, N.J., as-

signors to Engelhard Industries," Inc., Newark, N h, a corporationofDe'la'war'e FiledMay 26, 1965, Set. No. 459,010" 4'ClaimS. (Cl.260-345.l)

' AiisTRAcT on THE. DISCLOSURE Cyclic ethers are prepared from cyclicdiones by hydrogenation of 'the' dione in thepresence of an iridiumcataly'st. The cyclic ether products. of the disclosed process haveutility as'solvents for copolymers of the 'perfluorochloroolefins;

This invention relates to the preparation of cyclicethers and moreespeciallytoa new and improved process for the hydrogenation ofacyclicgamma or delta dionesto produce the corresponding cyclic ethercharacterized by a considerably enhanced hydrogenation rate. 7,

The process of this invention involves contacting an acyclic dione ofthe formula wherein each R is the same ordit'fer ent lower alkyl, i.e.l-4C inclusive alkyl,'-or: aryl radical, each R'is'a hydrogen atom orthe same or ditferent 'lower allcyl radicaL 'iLe', l-4 C inclusivealkyl, and n is an integerfjrom ,0-1, with hydrogen in the presence oran iridium catalyst. By reason of the iridium catalyst, thehydrogenation is etfected at a. considerably higherrate to-produce-thecorrespond- 3,408,364 Patented Oct. 29, 1968 production of thecorresponding cyclic ethers. Exemplary of the delta acyclic diones are2,6-heptanedione, 2,6-octanedione, 3,3-dimethyl-2,6-octanedione,3,4-dimethyl-2,6-heptanedione, 3,5-dimethyl-2,6-heptanedione,3-methyl-4-ethyl-2,6-octanedione,

3-nbutyl-2,6-heptanedione,

ing cyclic ether than ,is the case when utilizing a rhodium,

platinum, palladium or ruthenium catalyst. Acyclic diones suitable asfeed stocks herein include acyclic gamma diones of the formula t IWRHU...

' l l C 6 a B 5 wherein each R is'lower' alkyl, i.e. 1'4 C inclusive"'a1ltyl, or monoor bicyclic carbocylic' or heterocyclic 'aryl and each R"is hydrogen or lower alkyl, i;e. 14 C'inclirsive alkyl. Exemplaryof suchdiones are 2,5-h'exa'nedione, 2,5- octanedione, 3,6-octanedione,"2,5-heptam'zdione, 1,6-diphenyl 2,5 hexanedione, lphenyl=2,5-hexanedione, 4- methyl-2,5-hexanedione,3,4-dimethyl-2,5-hexanedione, 3, 3-dimethyl-4,4-diethyl-2,S-hexanedione,3,3-dimethyl-2,5- hexanedione, 1-a-naphthyl-2,5-hexanedione andl-fl-pyridyl-2,5-hexanedione. Product tetrahydrofurans obtained hereinby the hydrogenation of the above 'y-diketones are" respectively2,5-dimethyltetrahydrofuran, 2-methyl-5-propyltetrahydrofuran,2,S-diethyletrahydrofuran, 2-methyl-5-ethyltetrahydrofuran,2,S-dibenzyltetrahydrofuran, Z-methyl-S-benzyltetrahydrofuran2,3,S-trimethyltetrahydrofuran,

, 2,3,4,5-tetramethyltetrahydrofuran,

2,3,3,5-tetramethyl-4,4-diethyltetrahydrofuran,2,3,3,S-teti'amethyltetrahydrofuran, v v Z-methylS-u-naphthylmethyltetrahydrofuran and 2-methyl5-fi-pyridylmethyltetrahydrofuran.

Those substituents such as phenyl, napthyl or pyridyl which cantemselves be reduced, may be-reduced if the reduction be allowed tocontinue or some reduction of 4-isopropyl-2,6-heptanedione,3-methyl-2,6-heptanedione, 4-methyl-2,G-heptanedione,2-methyl-3,7-nonanedione, 1,7-diphenyl-2,6-heptanedione,l-flpyridyl-2,6-heptanedione and l-a-naphthyl-2,6-heptanedione.

Product tetrahydropyrans obtained herein by the hydro genation of theabove e-diketones are respectively 2,6-dimethyltetrahydropyran,2-methyl-6-ethyltetrahydropyran, 2,3,3-trimethyl-6-ethyltetrahydropyran,

2,3,4,6-tetramethyltetrahydropyran,

2,3,5,6-tetramethyltetrahydropyran,2,3-dimethyl-4,6-diethyltetrahydropyran,3-n-butyl-2,6-dimethyltetrahydropyran,4-isopropyl-2,6-dimethyltetrahydropyran, 2,3,6-trimethyltetrahydropyran,2,4,6-trimethyltetrahydropyran, 2-isopropyl-6-ethyltetrahydropyran,2,6-dibenzyltetrahydropyran, 2-methyl-G-fi-pyridylmethyltetrahydropyranand 2-methyl-6-a-naphthylmethyltetrahydropyran.

Hydrogenation conditions of temperature and pressure for the synthesisof the cyclic ethers herein are a temperature from about 25 C.-300 C.,and a pressure from about 1-1000 atmospheres. The hydrogen is suppliedto the reaction zone in the stoichiometric amount or in excess of thestoichiometric amount for reaction with the particular dione to producethe corresponding cyclic ether,

preferably the stoichiometric excess.

The iridium catalyst is supported or unsupported, preferably the former.Exemplary of solid catalyst support materials utilizable for preparingthe supported catalyst :are carbon, alumina, silica, kieselguhr, pumiceand calcium carbonate. The support may be in the form of pellets,granules, extruded shapes or powder. The supported iridum catalyst canbe prepared by precipitating a reducible compound of iridum, e.g.iridium oxide, onto the solid support material, by admixing an alkalinematerial, for instance an aqueous sodium hydroxide solution, with anaqueous solution of iridium chloride having the solid support materialtherein, followed by contacting the iridium oxide on the support atelevated temperature with a reducing agent, for instance hydrogen gas,to reduce the oxide to iridium metal. The iridium metal is present inthe supported catalyst in amount preferably from about O.llO% by Weight,more preferably about 0.55% by weight (based on catalytic metal plussupport),

3 The synthesis of a tetrahydrofuran compound by the hydrogenativecyclization of a gamma dione by its reaction with 2 moles of H isrepresented by the following equation ate the hydrogenation. Thereactionproduct when the Ir catalyst was utilized was identified as2,5-dimethyltetrahydrofuran by infrared spectrogram analysis.

The curves of the graph of the accompanying drawing also show theconsiderably increased rate of hydrogena- R R 6' tion achieved by thesupported iridium catalyst'of Test I I 2m R' R" 'Run'S of'thi'sexample,'designated'curve :A in" the It t 0 H H H2O graph, over thatprovided by'the' supported rhodiuincata- I lyst of Test Run 1,designated curve .Bf in. the graph, R R the supported platinum catalystof Te'stnRun 2, designated wherein each R and are as f i curve C in thegraph, the supported palladium catalyst Synthesis of a tetrahydropyranby the hy'drogenative of Test Run 3, desigtiated etlfve in the p andcyclization of a delta dione by its reaction with 2 moles t Supportedruthenium y fte'sign'ated Ftlrve of H is represented by the followingequation t ph the g ph a A P- J H2 P sure drop of the H 1n pounds persquare mch gauge of 180-200, designates .the reaction of 2 equivalentsof H with .10 ml. of dione, which is a molar ratio of about 2:1 of Hi tothe dione respectively, to produce the corresponding cyclic ether and-such was achieved in only about 3-4 minutes with Ir as catalyst (curveA). However, with the other platinum group-metals as catalysts, whereineach R and R are as aforesaid. the test runs were stopped afterconsiderably longer time The acyclic dione is preferably combined withan orperiods without 2' moles "of H havingr'eacted with the ganic liquidsolvent prior to the catalytic hydrogenating dione and due to either thehydrogenation rate falling off to provide a readily contactable dionefor the hydrogenconsiderably (the test runs of curves E, C and fB)ating. Exemplary of such solvents are cyclohexane, acetic or thehydrogenation rate being very slowthroughout the acid, lower alkanols,e.g. ethanol and propanol, and ethyl test (the test run of curve D)'.'acetate. These solvents are characterized by being inert to thehydrogenation and to the acyclic dione and prod- EXAMPLE H uct cyclicether. 2,5-hexancdione was hydrogenated in two separate test Thehydrogenative cyclization herein can be carried y a Procedure-Similar tothat of Example I eXeeePt out in a liquid phase batch or static systemor continuous that ethanol was the solvent instead of acetic acid andthe flow system, or a vapor phase continuous flow system. temperature inthe test nin'utililing a Supported Rh as The invention is furtherillustrated by reference to the catalyst was and in the test utilizingthe P following examples. Percentages are by weight. F t as" CatalystThe following results, Set

EXAMPLE I forth 1n Table II, were obtained. V 2,5-hexanedione washydrogenated in a number of sep- TABLE II arate test runs using adifferent platinum group metal as Rate catalyst in each run. Thehexanedione was admixed with 3 Catalyst gggg gg 33352 gm 53 7 glacialacetic ac1d as solvent therefor in an autoclave 7 (mg.) (ml.) I minute)equipped with a stirrer prior to the hydrogenation of each 6" Bil/Cm 610 20 5 test run, and the temperature and pressure for each test 7 5%Ir/0 300 s in 10 run was respectively 100 C. and 1000 p.s.i.g. Theparticular supported platinum group metal of the corresponding test runwas also charged into the autoclave in 4d The dafta of Table H Showthefate of H2 t or contact with the hexanedione in acetic acid. Hydrogendrogenatlon was more than 15 nmcs.faster wlth the gas was Supplied intothe autoclave from a Supply ported I r of Run 7as catalyst than with thesupportedtlh ervoir through a conduit equipped with a pmssure regw ofRun 6 as catalyst; even though the hydrogenation with later. As hydrogenreacted with the hexanedione in the the-Ir catalyst was effected at{temperature 50 lower autoclave additional hydrogen was f d into theauto. than that with the Rh catalyst as increased hydrogenation clave toreplace that which had reacted. By this method rates are generallyUbtained y increasing the hydrogenthe hydrogenation rates were obtainedat a constant presti n empe ature- Th rBa t n prod ct f Run 7 was sure.The following results, set forth in Table I, were identified as2,5-dimethyltetrahydrofuran by infrared obtained. spectrogram analysis.I 1

TABLE I Amount; Amount Amount Average Test Catalyst Catalyst 2,5-hex-Solvent Rate Hz Catalyst Run (.mg.) auedlone (ml.) Uptake Activity (ml.)(mL/min.)

1 5% Rh/C 600 5 20 8s ".08 1 PE] 600 10 10 100 .11 5% Pd/C 000 10 1o 24.03 5% Ru/C 600 10 10 153 .16 Lr/c 600 10 10 950 1.00

The Catalyst Activity column values were obtained by dividing the ratesof H uptake, i.e. reacted with the EXAMPLE HI 2,5-hexanedione, whenusing the indicated catalyst divided by the rate of H uptake when usingthe Ir cata- Fifty grams of l6-heptanedione is dissolved in lyst. Thedata of Table I show the considerably greater 250 ml. of methanol, andthe resulting solution mixed rate of H uptake or hydrogenation whenutilizing the supported Ir as catalyst in Test Run 5 than when using thesupported Rh, Pt, Pd or Ru as catalyst in Test Runs 1 2 3 and 4respectively. The TubleI data also show the considerably greateractivity of the Ir catalyst for together with 2 grams of iridium onalumina pellets containing 10 percent of iridium. This mixture is thenhydrogenated at -l00 C. and 500-1000 p.s.i.g. utilizing the apparatusutilized in Example 1, until 2'equivalents of hydrogen are absorbed. Theautoclave is then opened, the

vpyran isolated by fractional distillation.

When 3,6octanedione; 3-methyl-2,6:heptanedione; 4-methyl-2,6-heptanedione or 2-methyl-3,7 -nonanedione is hydrogenatedwhen dissolved in methanol and otherwise following the procedure ofExample I herein, theproduct obtained is respectively2,S-diethyltetrahydrofuran; 2,3,6 trimethyltetrahydropyran; 2,4,6trimethyltetrahydropyran; or 2-isopr'opy1-G-ethyltetrahydropyran. Theproduct cyclic ether in each case is isolated from the reaction productmixture by fractional distillation.

What is claimed is:

1. In a process for the preparation of cyclic ethers wherein an acyclicdione of the formu-la wherein each R is selected from the groupconsisting of lower alkyl and aryl, each R'is selected from the groupconsisting of hydrogen and lower alkyl and n is an integer from -1, is.hydrogenated and cyclized by contacting with hydrogen in the presence ofa hydrogenation catalyst at a temperature from about 25-300 C. and apressure from 1-1000 atmospheres, the improvement of using iridium asthe hydrogenation catalyst.

2,. The process of claim 1 wherein the iridium catalyst is supported ona solid catalyst carrier.

3. The process of claim 1 wherein the acyclic dione is 2,5-hexanedioneand the cyclic ether product is 2,5-dime ylte ahydrofuran. V, v

4, The process of claim 1 wherein the acyclic dione is 2,6-he'ptanedioneand the cyclic ether product is 2,6-dimethyltetrahydropyran.

References Cited UNITED STATES PATENTS 6/1953 Goldberg et al. 260-3461XR OTHER REFERENCES Theilheimer, Synthetic Methods of Organic-Chemistry," vol. II, Interscienee Pnb., New York ('149),p. 23.

Theilheimer, "Synthetic Methods of Organic Chemistry, vol. III,Karger,'New York '(1949), p. 21.

HENRY R. JILES, Primary Examiner.

J. M. FORD, Assistant Examiner.

